GASCO Precision Calibration Gas 44es-416X Mixture 200 PPM Carbon Monoxide, 20 PPM Hydrogen Sulfide, 18% Oxygen, Balance Nitrogen Contained in a 44L Liter ecosmart Factory Refillable Aluminum Cylinder, For Use with Any and All Gas Detectors, Cylinder Connection C-10, Calibration Certificate NIST, Made in the USA